Micromechanical devices (also called microelectromechanical (MEM) devices, micromachined devices, and nanostructures) are micron scale, three-dimensional objects constructed using semiconductor processing techniques. As used herein, the term micromechanical refers to any three-dimensional object that is at least partially constructed in reliance upon semiconductor processing techniques.
Micromechanical devices are utilized as fluid control devices. As used herein, the term fluid refers to either a gas or a liquid. Precise fluid control is important in many applications ranging from drug delivery to semiconductor processing equipment.
Micromechanical devices are used to form a variety of fluid flow control devices, including shut-off valves, pressure sensors, mass flow controllers, filters, purifiers, pressure gauges, and the like. FIG. 1 is a side cross-sectional view of a prior art device including a manifold 20 with an input port 22 and an output port 24. Mounted on the manifold 20 is a first micromechanical fluid control device 30 in the form of a normally open proportional valve and a second micromechanical fluid control device 32 in the form of a pressure sensor. Reference herein to a micromechanical fluid control device contemplates any device that is exposed to a fluid and operates to sense or control the fluid.
The first micromechanical fluid control device 30 includes a membrane 34 and a membrane control chamber 36. Fluid in the membrane control chamber 36 is selectively heated, thereby expanding the volume of the membrane control chamber 36, causing the membrane 34 to deflect and thereby obstruct fluid flow from the input port 22. By controlling the deflection of the membrane 34 in this manner, a proportional valve operation is achieved.
The second micromechanical fluid control device 32 also includes a membrane 38. The deflection of the membrane 38 is used to measure the pressure of the controlled fluid. Thus, the second micromechanical fluid control component 32 operates as a pressure sensor.
Each micromechanical fluid control component (30, 32) is mounted on the manifold 20 using a soft, compliant material 40, such as silicone or epoxy. Ideally, no stresses from the manifold 20 are transmitted to the fluid control components. Isolation of stresses is particularly important in the case of a pressure sensor (e.g. piezoresistive, capacitive, or strain pressure sensors). Pressure sensors are sensitive to the strain of the supporting structure (e.g., a manifold). In particular, if this strain changes over time, the signal produced by the sensor for a given pressure will change, thus decreasing the utility of the sensor.
Although soft, compliant materials have been used with some success, these materials are inappropriate for a large class of applications. In particular, these materials are inappropriate for use in the control and distribution of gases for semiconductor processing. In this context, the gases may be corrosive or toxic. The adhesive 40 between the manifold 20 and fluid control component 30, 32 must withstand this corrosive and/or toxic substance so that there is no observable change in the functionality of the adhesive 40.
Furthermore, semiconductor processing equipment also requires a high level of cleanliness. The fluid control components and their attachment material must not measurably alter the character of the controlled fluid. This limitation eliminates many soft, compliant materials from consideration as candidates for component attachment.
Ideally the adhesive is hermetic. However, hermetic seals are typically quite hard, and therefore transfer package stress directly to the micromechanical fluid control component. The adhesive should also be stable, such that signal drift does not develop over time.
In view of the foregoing, it would be highly desirable to provide an improved technique for mounting fluid control components. Ideally, such a technique would provide a stable, hermetic, clean, and corrosion resistant interface between a fluid control component and a manifold.